The fabrication of drill bits utilized in hydrocarbon drilling is a highly refined and competitive field. Drill bits utilized for boring wells many thousands of feet, and even miles, into the earth are required to be extremely effective and highly reliable to reduce the time necessary to drill such bore holes. It can be appreciated that with nominal drilling expenses of about $5,000 an hour, any down time required to repair or change a drill bit can be extremely costly.
The standard earth boring drill bit includes three arms connected to a threaded stem, with each arm supporting a toothed cone rotating thereon. Thus, as the bit is turned by the drill string, the toothed cones also rotate individually to grind a bore hole through the earth formation and thereby drill the well. An area of constant concern with such drill bits is that of the bearing surfaces and the fluid seal which must be maintained between the toothed cone and the arm.
U.S. Pat. No. 4,207,658, assigned to Dresser Industries, discloses a drill bit with special wear resistant bearing surfaces between the toothed cone and the drill bit arm to increase the life span and reliability of the bit. An internal static lubrication system is formed between each toothed cone and arm of the drill bit to provide the required lubrication during the rotary action of the drill bit. An O-ring type of elastomer generally provides a seal between the toothed cone and the drill bit arm to isolate the internal lubrication system from the harsh environment of the bore hole. A long-lasting and reliable seal is often difficult to achieve, in view that the drill bit operates continuously in an abrasive environment of drill mud and earth formation chips, as well as operating in caustic chemicals which are often injected into the well.
The life of drill bits have been extended by the development of various techniques for providing hardened bearing surfaces between the toothed cone and the drill bit arm. U.S. Pat. Nos. 4,655,851; 4,012,238; 4,102,838; 4,188,242 and 3,922,038 disclose techniques for fabricating extremely hard bearing surfaces to thereby extend the life of the drill bits. Particularly, carburizing and boronizing techniques are disclosed in the noted patents for achieving a highly wear resistant bearing surface. U.S. Pat. No. 4,248,485, assigned to Dresser Industries, illustrates yet another refinement in the drill bit art, in which hardened inlaid areas are formed in the journal bearing arm to also extend the life of the drill bit. A wear resistant and antigalling bearing disclosed in the noted U.S. Pat. No. 4,207,658 provides an excellent combination of a hardened bearing surface and a porous matrix bearing to enhance the life span of the bit.
Attempts continue to be made to improve the quality of the seal between the toothed cones and the drill bit arms. The seal surface on the drill bit arm is preferably constructed with a hardened surface so that the constant rotation of the elastomer seal thereon does not wear an annular groove in the surface and reduce the effectiveness of the seal. In the noted U.S. Pat. No. 4,655,851, an enclosure structure and technique is disclosed so that the seal surface can be carburized, while the bearing surfaces are boronized. While attempts have been made to boronize the seal surface itself to provide a wear resistant surface, the resulting rough surface tends to wear the elastomeric seal. In addition, boronizing the seal surface requires additional heat treatment and thus more process steps.
It can be seen that a need exists for an improved drill bit seal arrangement which can extend the life of the drill bit, without compromising the quality of the bearing surfaces. An associated need exists for a fabrication technique for constructing the seal apparatus separate and apart from the journal bearing surface, such that each process and resulting structure can be optimized.